The invention relates to print hammer operation in printers, and more particularly, to a device that stabilizes rebounding of the print hammer during printer operation.
A conventional plunger-type printer is illustrated in FIG. 5. A sectional view of the mechanical configuration of such a printer illustrates a platen (2), a sheet of paper (3), and a ribbon (4) inserted between a type character (5) and the paper (3). A daisy-wheel (6) which provides type characters at its circumference frame (7) holds and positions the print hammer (9). Print hammer (9) has an end (12), a tip (10), a spring stopper (11) and is driven by a solenoid hammer coil (13). Front flange (14) and rear flange (15) support the print hammer (9).
In the prior art system illustrated by FIG. 5, a spring (16) is installed between the spring stopper (11) of the print hammer (9) and the front flange (14). Back-stopper (17) controls the print hammer's rebound action.
In this configuration, when the solenoid coil (13) drives the hammer (9), the tip (10) pushes the type character (5) against the ribbon (4), printing the character on the paper (3). Spring (16) is compressed during this time. After printing the character, spring (16) restores hammer (9) to its original position. Printing is thus performed by the reciprocating action of hammer (9).
Where a plunger-type print hammer is used in daisy-wheel printers, the temperature at the print hammer back-stopper may rise between 50 and 70 degrees Celsius during operation. However, the restitution coefficient of the material used for the back-stopper in conventional printers varies as the temperature varies, as illustrated in FIG. 6. Many kinds of elastomers are selected for use as back-stoppers. However, in conventional printers, when the print hammer (9) is restored to its original position by the force of the spring (16) after the printing action, a strong rebounding action may take place when the rear end of the print hammer (9) strikes the back-stopper (17), especially when the coefficient of restitution has increased. This hammer rebounding may cause the print hammer to restrike the type character (5) and interfere with the movement of the type (5). A back stopper material whose coefficient of restitution did not vary with its temperature would eliminate these problems, but it was difficult to find such kinds of materials.
It is therefore an object of the invention to stabilize the rebounding action of a print hammer despite rising temperatures of the print hammer and back-stopper.
It is a further object of the invention to provide a back-stopper material whose restitution coefficient does not significantly vary with its temperature and thus does not impair the printer's operation.